Hybrid Battery Relay Contactor Guide
Understanding the relays and contactors that control your hybrid battery.
What Are System Main Relays?
System Main Relays (SMRs) are high-voltage contactors that connect and disconnect the hybrid battery from the vehicle’s electrical system. They are critical safety components that isolate the high-voltage battery when the vehicle is off or during a fault.
- SMR function: Connect/disconnect battery from inverter
- SMR location: Inside battery pack junction box
- Related codes: P0A1F, P0A78, P0A93
Relay Failure Symptoms
When SMRs fail, the vehicle may not enter READY mode, or it may shut down while driving. In Phoenix, heat and electrical stress can cause relay contacts to weld or burn. This can sometimes be misdiagnosed as a battery failure.
Relay vs Battery Failure
If you’re seeing P0A1F or P0A78 but not P0A80 or P3011–P3024, the issue may be relay-related rather than battery-related. Hybrid Matters can diagnose the root cause. If the battery is the problem, we offer 28-cell replacement from $800 and 34-cell replacement from $1,000.
We service Toyota Prius (Gen 2 2004–2009, Gen 3 2010–2015), Camry Hybrid (2007–2017), Avalon Hybrid (2013–2018), Nissan Altima Hybrid (2007–2011), Lexus ES 300h (2013–2018), and Lexus CT 200h (2011–2017).
Schedule Diagnostics
Call (602) 845-9291 or book online for mobile hybrid diagnostics in Phoenix.
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